I use Perl at work, largely due to that being what much of our legacy code is written in, however it's not something I interviewed for or was searching for explicitly. Personally, I've only used the language in any capacity over the last two years, and I would say that it is worth learning. If nothing else, I've gotten some good practice with a fun language that I would not have learned otherwise.
For Perl 5 vs 6, 5 is the stable release that you will want to work with. 6 is still being developed, and I certainly don't see it replacing Python any time soon. Give it a shot if you have some time, it's a useful tool to have in your belt.